Hi:
I'm working in the same way and it's running OK.
Here is a little HOW-TO:
NT box: Nothing to make. If you can connect from any client that'all.
Linux box:
Must have an oracle client installed. Oracle haven't client software CD or package. You must get the Enterprise Server for Linux and install it but only the software ( don't create database ). The Enterprise Edition for developers can be downloaded from technet.oracle.com. Once installed you must make the oracle user public, putting the oracle environment variables ( ORACLE_HOME, ORACLE_BASE, ORA_NLS33, etc... ) in the /etc/profile of the Linux box. The directory tree of the oracle software must have rigths set to 664 ( All users can read and execute any file of the oracle user ). Define the TNSNAMES.ORA entry for the NT instance. To test all of this any user should be able to make an 'sqlplus username/password@ora_service_name without problems. If all of this is correct then you must compile the php to be able to use the oracle software ( for example with the --with-oracle=(copy this the 'echo $ORACLE_HOME' ).
This works very well for me.
E-mail me for more specific information.